Method and device for feeding back downlink channel feedback information, and method and device for user pairing

ABSTRACT

A method and device for feeding back downlink channel feedback information, and a method and device for user pairing. The method for feeding back downlink channel feedback information includes: calculating the multi-user channel quality indication error of a user, which error is used to reflect the difference in channel quality indication between the situation of multi-user multiple input multiple output transmission and the situation of single user multiple input multiple output transmission; adding the multi-user channel quality indication error into the downlink channel feedback information which includes a pre-coding matrix indication and a channel quality indication, and feeding the same back to a base station for scheduling. Therefore, the bit error rate of demodulation in the MIMO system can be reduced and the system performance can be improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/362,707, filed Mar. 25, 2019, which is a continuation of U.S. patentapplication Ser. No. 13/878,581, filed Apr. 10, 2013 (now U.S. Pat. No.10,298,297), which is based on PCT filing PCT/CN2011/081111, filed Oct.21, 2011, and claims priority to CN 201010544399.1, filed Nov. 5, 2010,the entire contents of each are incorporated herein by reference.

FIELD OF THE INVENTION

The disclosure generally relates to a communication field, in particularto feeding back downlink channel feedback information of a user in aMultiple Input Multiple Output, MIMO, communication system and userpairing of a base station.

BACKGROUND OF THE INVENTION

In MIMO system, multi-antenna transmission is divided into single userMIMO (SU-MIMO) transmission mode and multi-user MIMO (MU-MIMO)transmission mode.

As shown in FIG. 1, in the SU-MIMO transmission, a base station (BS)sends a plurality of data streams on the same time-frequency resource tothe same user. In contrast, in the MU-MIMO transmission, a base station(BS) sends a plurality of data streams on the same time-frequencyresource to different users, and improves the system capacity bytransmitting data simultaneously to a plurality of users.

Pre-coding technology is a signal processing technology whichpre-processes the transmitted symbols at the transmitting side by usingchannel state in order to eliminate interference, improve systemcapacity and the like. The pre-coding needs the base station to knowtransmission channel information and determine a pre-coding matrix basedon the transmission channel information. For example, pre-codingtechnology may be a pre-coding technology based on codebook, in whichthe codebook is the same with respect to user equipment (UE) and basestation (BS). A user notifies a base station of the pre-coding matrixused by the user by feeding back a pre-coding matrix indication (PMI) tothe base station.

In MIMO transmission technology using the pre-coding technology, the PMImay be included in downlink channel feedback information which a userneeds to feed back to a base station. The downlink channel feedbackinformation is information for reflecting the downlink channel statewhich the user feeds back to the base station through uplink channel.

In MIMO systems of LTE, for example, in downlink channel feedback ofSU-MIMO, the downlink channel feedback information which a user feedsback to a base station may includes: the PMI for indicating a pre-codingmatrix; and a feedback channel quality indication (CQI) for selecting amodulation coding mode of transmission data by the base station. In LTEstandards, in the situation of MU-MIMO transmission, the PMI and CQI inthe downlink channel feedback information which a user feeds back to abase station is obtained by optimizing the PMI and CQI in the situationof SU-MIMO transmission. However, using the PMI obtained in thesituation of SU-MIMO transmission in MU-MIMO transmission may induceinfluence to the selection of paired user in MU-MIMO transmission andthus influence to the communication performance.

In addition, from the perspective of base station side, after the userfeeding back the downlink channel feedback information, the base stationdetermines whether the MU-MIMO transmission or the SU-MIMO transmissionis used according to the downlink channel feedback information. As forSU-MIMO transmission, the base station obtains the pre-coding matrixaccording to the PMI in the downlink channel feedback information, andselects a suitable modulation coding mode for the user according to theCQI in the downlink channel feedback information. As for MU-MIMOtransmission, the base station needs to first select paired user(s) forthe user according to the downlink channel feedback information fed backby the user, and then obtain a pre-coding matrix for the user and selecta suitable modulation coding mode for the user according to the PMI andCQI included in the downlink channel feedback information fed back byindividual paired users selected for this user.

SUMMARY OF THE INVENTION

A brief summary about the present disclosure is provided hereinafter toprovide basic understandings related to some aspects of the presentdisclosure. It shall be understood that this summary is not anexhaustive summary related to the present disclosure. The summary is notintended to determine a key part or an important part of the presentdisclosure, nor does it intend to limit the scope of the presentdisclosure. The purpose of the summary is only to provide some conceptsin simplified forms to prelude more detailed descriptions discussedlater

One object of the disclosure is to provide feeding back of downlinkchannel feedback information, which may further increase information forrepresenting the quality indication error caused by the user parametererrors (such as the signal to noise ratio (SNR), synchronizationdifference, location difference and the like) in the MU-MIMOtransmission in the downlink channel feedback information, in thedownlink channel feedback of the MU-MIMO transmission, thereby toachieve feeding more accurate downlink channel feedback information backto the base station. Moreover, the base station may obtain CQI andmodulation coding mode more suitable for the user in a more accuratemanner. Therefore, the demodulation error code rate may be reduced andthe system performance may be improved.

Correspondingly, the other object of the disclosure is to provide userpairing at base station side, which uses information for representingthe quality indication error caused by the parameter errors (such as thesignal to noise ratio, synchronization difference, location differenceand the like) of the user in the MU-MIMO transmission, thereby toachieve more accurate modulation coding and pairing. Therefore, thedemodulation error code rate of the user may be reduced and the systemperformance may be improved.

Therefore, one embodiment of the disclosure provides a method forfeeding back downlink channel feedback information of a MIMOcommunication system, comprising: calculating a multi-user channelquality indication error of a user in the system by the user, themulti-user channel quality indication error is used to reflect thedifference in channel quality indication between the situation ofmulti-user multiple input multiple output transmission and the situationof single user multiple input multiple output transmission; and addingthe multi-user channel quality indication error to the downlink channelfeedback information including a pre-coding matrix indication and achannel quality indication, and feeding the same back to a base stationfor scheduling of the user.

Another embodiment of the disclosure provides a method for user pairingof MIMO, comprising: a downlink channel feedback information receivingstep of receiving downlink channel feedback information from a user, thedownlink channel feedback information includes a pre-coding matrixindication, a channel quality indication, and a multi-user channelquality indication error, wherein the multi-user channel qualityindication error is used to reflect the difference in channel qualityindication between the situation of MU-MIMO transmission and thesituation of SU-MIMO transmission of the user; an initial paired userselecting step of selecting the user with the minimum multi-user channelquality indication error from transmitting users as an initial paireduser, the transmitting users include all the current transmitting userswhich are allowed to enter a multi-user multiple input multiple outputtransmission mode; a correlation calculating step of calculating thecorrelation of each paired user to each of other transmitting users, andselecting one or more users from the other transmitting users ascandidate paired user(s) according to the correlation; a paired userselecting step of selecting paired user(s) from the candidate paireduser(s) according to the multi-user channel quality indication error;and repeating the correlation calculating step and the paired userselecting step until a predetermined number of paired users have beenselected.

Another embodiment of the disclosure provides a method for communicationin a Multiple Input Multiple Output system, comprising: feeding downlinkchannel feedback information back to a base station by a user; decidingby the base station whether a single user multiple input multiple outputtransmission mode or a multi-user multiple input multiple outputtransmission mode is used; obtaining a pre-coding matrix of the user byusing a pre-coding matrix indication in the fed back downlink channelfeedback information, and selecting a modulation coding mode for theuser by using a channel quality indication in the fed back downlinkchannel feedback information, by the base station, in case of using thesingle user multiple input multiple output transmission mode; andexecuting pairing for the user, obtaining a pre-coding matrix for themulti-user multiple input multiple output transmission mode based on thepre-coding matrix indication in the downlink channel feedbackinformation fed back by the user and the paired user(s) thereof, andselecting modulation coding mode corresponding to each user based on thechannel quality indication and the multi-user channel quality indicationerror in the downlink channel feedback information fed back by the userand paired user(s) thereof, by the base station, in case of using themulti-user multiple input multiple output transmission mode; wherein theuser uses the method for feeding back as described above to feed thedownlink channel feedback information back to the base station, and thebase station uses the method for user pairing as described above toexecute user pairing.

In addition, one embodiment of the disclosure provides an apparatus forfeeding back downlink channel feedback information of a MIMOcommunication system, comprising: a multi-user channel qualityindication error calculating unit configured to calculate a multi-userchannel quality indication error of a user, wherein the multi-userchannel quality indication error is used to reflect the difference inchannel quality indication between the situation of multi-user multipleinput multiple output transmission and the situation of single usermultiple input multiple output transmission of the user; and a downlinkchannel feedback information feeding back unit configured to add themulti-user channel quality indication error to the downlink channelfeedback information including a pre-coding matrix indication and achannel quality indication, and feeding the same back to a base stationfor scheduling.

One embodiment of the disclosure provides an apparatus for user pairingof a MIMO communication system, comprising: a downlink channel feedbackinformation receiving unit configured to receive downlink channelfeedback information from a user, wherein the downlink channel feedbackinformation includes a pre-coding matrix indication, a channel qualityindication, and a multi-user channel quality indication error, whereinthe multi-user channel quality indication error is used to reflect thedifference in channel quality indication between the situation ofmulti-user multiple input multiple output transmission and the situationof single user multiple input multiple output transmission of the user;an initial paired user selecting unit configured to select the user withthe minimum multi-user channel quality indication error fromtransmitting users as a paired user, the transmitting users include allthe current transmitting users which are allowed to enter a multi-usermultiple input multiple output transmission mode; a correlationcalculating unit configured to calculate the correlation of each paireduser to each of other transmitting users, and selecting one or moreusers as candidate paired user(s) according to the correlation; a paireduser selecting unit configured to select paired user(s) from thecandidate paired user(s) according to the multi-user channel qualityindication error; and the correlation calculating unit and the paireduser selecting unit are configured to repeat their operations until apredetermined number of paired users have been selected.

In addition, an embodiment of the disclosure further provides a userequipment comprising the apparatus for feeding back downlink channelfeedback information as described above and a base station comprisingthe apparatus for user pairing as described above, and a communicationsystem comprising at least one above user equipment and at least oneabove base station.

An embodiment of the disclosure also provides a computer program codewhen executed by a computing device to cause the computing device toperform the processes of any of above methods, a computer readablestorage medium on which the computer program code is stored, and acomputer program product.

Those and other advantages of the disclosure will be more apparent bydetail explanations of the best embodiments of disclosure provided byreferring to the Figure.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood better by referring to descriptionprovided in conjunction with the drawings, wherein the same or similarreference signs are used to represent the same or similar components inall of the Figures. The Figures and the following detailed descriptionare included in the Description and form a part of the Description, andthey are used to further explain preferable embodiments of thedisclosure and explain principle and object of the disclosure byexamples. In the Drawings:

FIG. 1 is a schematic diagram illustrating the situation of SU-MIMO andthe situation of MU-MIMO;

FIG. 2 is a flowchart illustrating a method for feeding back downlinkchannel feedback information according to an embodiment of thedisclosure;

FIG. 3 is a flowchart illustrating a process for calculating themulti-user channel quality indication error according to the signal tonoise ratio according to an embodiment of the disclosure;

FIG. 4 is a flowchart illustrating a process for user pairing accordingto an embodiment of the disclosure;

FIG. 5 is a flowchart illustrating a communication method in a MIMOsystem according to an embodiment of the disclosure;

FIG. 6 illustrates an apparatus for feeding back downlink channelfeedback information of a MIMO system according to an embodiment of thedisclosure;

FIG. 7 is a schematic diagram illustrating a multi-user channel qualityindication error calculating unit according to an embodiment of thedisclosure;

FIG. 8 illustrates an apparatus for user pairing in MU-MIMO transmissionmode in a MIMO system according to an embodiment of the disclosure; and

FIG. 9 is a block diagram illustrating an example structure of auniversal personal computer that may implement the methods and/orapparatuses according to embodiments of the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Example embodiments of the disclosure will be described in conjunctionwith the Figures. For the sake of clearness and conciseness, thedescription does not describe all features of the actual embodiments.However, it shall be understood that decisions specific to embodimentshave to be made in a procedure of developing such an actual embodimentto achieve the specific object of the developer, for example, complyingwith limited conditions relative to system and transaction, and thoselimited conditions may change in different embodiments. In addition, itshall be understood that although the developing working may be complexand time consuming, such a developing working is only routine for thoseskilled in the art benefit from the disclosure of the disclosure.

In addition, it shall be noted that, to avoid blurring of the disclosuredue to unnecessary details, only device structures and/or process stepsclosely related to the solution of the disclosure are illustrated in thedrawings, and other details not closely related to the disclosure areomitted.

FIG. 2 is a flowchart illustrating a method for feeding back downlinkchannel feedback information according to an embodiment of thedisclosure.

As shown in FIG. 2, at step S202, a user in a MIMO system calculates amulti-user channel quality indication error of the user.

Herein, the multi-user channel quality indication error may reflect theerror in channel quality indication between the situation of MU-MIMOtransmission and the situation of SU-MIMO transmission of the user. Sucherror may be caused by the parameters difference (such as the signal tonoise ratio, synchronization difference, location difference and thelike) of the user in the MU-MIMO transmission.

Next, at step S204, the user in the MIMO system feeds the multi-userchannel quality indication error back to a base station along with thedownlink channel feedback information.

Herein, as specified in LTE, the downlink channel feedback informationwhich the user feeds back to the base station may include: the PMI forindicating a pre-coding matrix; and CQI for selecting a modulationcoding mode of transmission data by the base station.

Herein, the user may use various known methods to obtain the PMI and CQIin the downlink channel feedback information.

For example, the user may find out a pre-coding matrix corresponding tothe user based on the measured channel information matrix, and thengenerate the PMI for representing the pre-coding matrix. In addition,the user may obtain the value of related CQI based on the measuredsignal to noise ratio, for example.

As can be seen, in the method for feeding back downlink channel feedbackinformation according to above embodiment, the multi-user channelquality indication error is further fed back to the base station, sothat the error in channel quality indication between the situation ofMU-MIMO transmission and the situation of SU-MIMO transmission of theuser may be reflected more accurately.

In this way, the user feeds more accurate downlink channel feedbackinformation back to the base station, so that the base station mayobtain CQI and modulation coding mode more suitable for the user in amore accurate manner. Therefore, the demodulation error code rate of theuser may be reduced in the communication system and the systemperformance may be improved.

In above method, the multi-user channel quality indication error may becalculated by considering various parameters and using any suitablemethod.

For example, in a specific embodiment of the disclosure, the multi-userchannel quality indication error may be calculated based on the signalto noise ratio.

FIG. 3 is a flowchart illustrating a process for calculating themulti-user channel quality indication error according to the signal tonoise ratio according to an embodiment of the disclosure.

As shown in FIG. 3, a measuring is executed at step S302.

Specifically, a user may measure the channel state thereof, thereby toobtain channel information matrix and the signal to noise ratio of theuser.

The user may obtain the pre-coding matrix of the user based on themeasured channel information matrix.

For example, the pre-coding matrix may be obtained with the measuredchannel information matrix based on the following equation (1).

$\begin{matrix}{b = {\arg\limits_{{i = 1},\ldots,B}\max{{{H\bullet w}_{i}}/{H}}}} & (1)\end{matrix}$

In equation (1), H represents the measured channel information matrix ofthe user, w_(i) represents the pre-coding matrix, i represents thelocation of the pre-coding matrix in codebook, by which the pre-codingmatrix can be obtained from the codebook, and the size of the codebookis B.

Next, at step S304, quantization error may be calculated.

Herein, the quantization error is a parameter reflecting the errorbetween the measured channel information matrix and the obtainedpre-coding matrix.

The quantization error may be represented according to the channelinformation matrix and the pre-coding matrix.

For example, the quantization error may be calculated according to thefollowing equation (2).

$\begin{matrix}{e = \frac{{H^{H}w_{i}}}{{H} \times {w_{i}}}} & (2)\end{matrix}$

In equation (2), the meaning of H and w_(i) are the same to that inequation (1), and e represents the quantization error.

Next, as shown in FIG. 3, at step S306, the minimum interference levelto the user is calculated.

Specifically, out of all the potential paired users to which the usermay pair, the user with the minimum interference level to the user isfound out, and the minimum interference level is calculated.

Herein, the potential paired users may be users meeting an orthogonalcondition, for example, and the orthogonal condition may be that thepre-coding matrix corresponding to a potential paired user is orthogonalto the pre-coding matrix of the user, for example.

For example, the minimum interference level may be calculated accordingto the following equation (3).

$\begin{matrix}{a = {\min\limits_{{w_{j}*w_{i}^{H}} = 0}\left( {{H^{H}w_{i}}} \right)}} & (3)\end{matrix}$

In equation (3), w_(j) represents the pre-coding matrix of any potentialpaired user, the meaning of H and w_(i) are the same to that in equation(1), and a represents the minimum interference level. In equation (3),w_(j)*w_(i) ^(H)=0 represents the orthogonal condition.

Next, as shown in FIG. 3, at step S308, the signal to noise ratio of theuser in the situation of multi-user is calculated.

Specifically, the above quantization error, the measured minimuminterference level and the signal to noise ratio may be used tocalculate the signal to noise ratio of the user in the situation ofmulti-user.

For example, the signal to noise ratio in the situation of multi-usermay be calculated based on the following equation (4).

$\begin{matrix}{{SNR}_{{MU} - {MIMO}} = \frac{{{SNR}/2} \times (e)^{2}}{{{{SNR}/2} \times a^{2}} + 1}} & (4)\end{matrix}$

In equation (4), SNR represents the signal to noise ratio measured bythe user, SNR_(MU-MIMO) represents the evaluated signal to noise ratioof the user in the situation of multi-user, e represents thequantization error, and a represents the minimum interference level.

Next, with reference to FIG. 3, at step S310, multi-user channel qualityindication error of the user in the situation of multi-user MIMOtransmission may be calculated.

Specifically, the multi-user channel quality indication error may becalculated based on the signal to noise ratio measured by the user andthe above calculated signal to noise ratio in MU-MIMO mode.

For example, the multi-user channel quality indication error may becalculated based on the following equation (5).

V=CQI(SNR)−CQI(SNR_(MU-MIMO))   (5)

In equation (5), SNR represents the signal to noise ratio measured bythe user, SNR_(MU-MIMO) represents the calculated signal to noise ratioof the user in the situation of MU-MIMO transmission; CQI( ) representschannel quality indication function related to the signal to noiseratio; and V represents the multi-user channel quality indication errorof the user.

In this way, the multi-user channel quality indication error of the userin the situation of MU-MIMO transmission may be calculated based on thesignal to noise ratio.

In the above description, the calculation of the multi-user channelquality indication error is explained by only taking the signal to noiseratio as an example, however, the above description is only an example,and the disclosure is not limited to this. For example, the calculationof the multi-user channel quality indication error may be executed byconsidering the influence of the other parameters (for example, timeparameters (such as time synchronization difference), locationparameters, and the like). For example, the calculation of themulti-user channel quality indication error may also be implementedbased on time parameters, or based on a combination of time parametersand the signal to noise ratio.

Correspondingly, an embodiment of the disclosure also provides a methodof user pairing in MU-MIMO transmission mode of a MIMO system which isimplemented at base station side.

FIG. 4 is a flowchart illustrating a method for user pairing in MU-MIMOtransmission mode in a MIMO system according to an embodiment of thedisclosure.

As shown in FIG. 4, at step S402, a base station receives downlinkchannel feedback information from a user.

In embodiments of the disclosure, the downlink channel feedbackinformation may include pre-coding matrix indication, channel qualityindication, and multi-user channel quality indication error, wherein themulti-user channel quality indication error is used to reflect thedifference in channel quality indication between the situation ofmulti-user multiple input multiple output transmission and the situationof single user multiple input multiple output transmission of the user.

As a preferable example, the multi-user channel quality indication errormay be calculated with the method according to the above embodiments ofthe disclosure.

Next, at step S404, the base station selects an initial paired user fromtransmitting users.

Preferably, the base station may select the user with the minimummulti-user channel quality indication error from the transmitting usersas an initial paired user, for example.

In this specification, the transmitting users may be defined as one ormore users which are allowed to enter a multi-user multiple inputmultiple output transmission mode out of the users being transmittingdata currently.

The base station may decide whether a certain user may enter the MU-MIMOtransmission mode (that is, decide the transmitting user) by using anexisting decision strategy, for example, based on channel condition,rate requirement, current resource allocation, and the like of the user.

Next, at step S406, the base station calculates the correlation of eachpaired user to each of other transmitting users, and selects one or moreusers from the other transmitting users as candidate paired user(s)according to the correlation.

The correlation between two users may be calculated by using any knownmethod.

For example, the correlation of each paired user to each of othertransmitting users may be calculated by using the following equation(6).

$\begin{matrix}{\rho = \frac{{w_{1}w_{2}^{H}}}{{w_{1}} \times {w_{2}}}} & (6)\end{matrix}$

In the equation (6), w1 represents the pre-coding matrix of a paireduser, and w2 represents the pre-coding matrix of a transmitting user,the pre-coding matrix of each user may be obtained according to PMI inthe downlink channel feedback information fed back by the each user.

After calculating the correlation, the base station may select one ormore users from the other transmitting users as the candidate paireduser(s) according to the calculated correlation.

In an example, the base station may select one or more users with thecorrelation below a predetermined threshold as the candidate paireduser(s).

In another example, the base station may also select one or more userswith the minimum correlation as the candidate paired user(s).

Next, at step S408, the base station select a paired user from thecandidate paired user(s).

Specifically, the base station may select according to the multi-userchannel quality indication error of individual candidate paired user(s).

For example, the base station select a candidate paired user with theminimum multi-user channel quality indication error in the fed backdownlink channel feedback information from the candidate paired user(s)as the paired user.

Next, at step S410, the base station decides whether a predeterminednumber of paired users have been selected.

If the number of the paired user selected by the base station has notreached the predetermined number, the steps S406 and S408 are repeatedin order to select other paired users from the transmitting users, untilthe required number of paired users has been selected.

If the number of the paired user selected by the base station hasreached the predetermined number, the pairing process ends.

In the above user pairing process, the base station uses the multi-userchannel quality indication error fed back by the user. In this way, inthe MU-MIMO transmission mode, the base station may implement moreaccurate pairing. Therefore, the system performance may be improved.

In addition, an embodiment of the disclosure provides a communicationmethod in a MIMO system with the method for feeding back downlinkchannel feedback information according to the above embodiments of thedisclosure and the method for user pairing according to the aboveembodiments of the disclosure.

FIG. 5 is a flowchart illustrating a communication method in a MIMOsystem according to an embodiment of the disclosure.

As shown in FIG. 5, at step S502, a user feeds downlink channel feedbackinformation back to a base station.

For example, the user may feed the downlink channel feedback informationback to the base station according to the method for feeding backdownlink channel feedback information according to the above embodimentsof the disclosure.

In this case, the downlink channel feedback information fed back by theuser may include PMI, CQI, and multi-user channel quality indicationerror, wherein the multi-user channel quality indication error mayreflect the difference in channel quality indication between thesituation of MU-MIMO transmission and the situation of SU-MIMOtransmission of the user.

Specifically, the user may calculate the multi-user channel qualityindication error according to equations (1)-(5).

Next, at step S504, the base station decides whether a SU-MIMOtransmission mode or a MU-MIMO transmission mode is used.

The base station may decide whether the SU-MIMO transmission mode or theMU-MIMO transmission mode is used according to an existing decisionstrategy.

For example, the base station may decide whether the SU-MIMOtransmission mode or the MU-MIMO transmission mode is used according toone or more factors of channel condition, rate requirement, currentresource allocation of the user, and the like.

With reference to FIG. 5, in case that the base station decides to usethe SU-MIMO transmission mode, the base station may obtain a pre-codingmatrix based on pre-coding matrix indication in the downlink channelfeedback information fed back by the user, and select a modulationcoding mode for the user based on the CQI in the downlink channelfeedback information, and the base station does not use the multi-userchannel quality indication error for the MU-MIMO transmission mode inthe downlink channel feedback information fed back by the user.

With reference to FIG. 5, in case that the base station decides to usethe MU-MIMO transmission mode, at step S508, the base station may selecta paired user for the user.

For example, the base station may select the paired user for the useraccording to the method for user pairing according to the aboveembodiments of the disclosure. As for the detailed specific of theprocess for selecting the paired user, the above description withrespect to FIG. 4 may be referred to, and thus will not be repeated forsimplicity of the specification.

Next, at step S510, the base station calculates the pre-coding matrix inthe MU-MIMO transmission mode and selects the suitable modulation codingmode for individual paired users.

For example, the base station may obtain the pre-coding matrix in theMU-MIMO transmission mode based on the pre-coding matrixes of individualpaired users (which can be obtained with the PMI fed back by individualpaired users), and select the modulation coding mode for individualpaired users based on the CQI and multi-user channel quality indicationerror of individual paired users.

For example, the base station may obtain the pre-coding matrixcorresponding to each paired user according to the PMI of the eachpaired user, and then the base station may further obtain the pre-codingmatrix in the MU-MIMO transmission mode based on these pre-codingmatrixes.

For example, the pre-coding matrix in the MU-MIMO transmission mode maybe obtained based on the following equation (7)

G=[w ₁ , w ₂]([w ₁ , w ₂]^(H) [w ₁ , w ₂])⁻¹   (7)

In equation (7), G represents the pre-coding matrix in the MU-MIMOtransmission mode, w1 represents the pre-coding matrix corresponding tothe user, and w2 represents the pre-coding matrix corresponding to thepaired user.

In addition, the base station may calculate the CQI of a paired user inthe MU-MIMO mode based on the CQI and the multi-user channel qualityindication error in the downlink channel feedback information of thepaired user, and accordingly select a modulation coding mode for theuser.

For example, the CQI of the user in the MU-MIMO mode may be calculatedaccording to the CQI and the multi-user channel quality indication erroraccording to the following equation (8).

CQI_(MU-MIMO)=CQI−V   (8)

In equation (8), CQI_(MU-MIMO) represents the channel quality indicationof the paired user in the MU-MIMO transmission mode, CQI represents thevalue of the CQI included in the downlink channel feedback informationof the paired user, and V represents the multi-user channel qualityindication error in the downlink channel feedback information of thepaired user.

In this way, in the MIMO system using the communication method accordingto the above embodiments of the disclosure, since the difference inchannel quality indication between the situation of MU-MIMO transmissionand the situation of SU-MIMO transmission of the user has beenconsidered, the demodulation bit error rate of the user in the MIMOtransmission mode can be reduced and the system performance can beimproved.

In addition, according to the embodiments of the disclosure, apparatusescorresponding to the methods are also provided.

FIG. 6 illustrates an apparatus for feeding back downlink channelfeedback information of a MIMO system according to an embodiment of thedisclosure.

As shown in FIG. 6, the apparatus for feeding back downlink channelfeedback information 600 according to an embodiment of the disclosurecomprises a multi-user channel quality indication error calculating unit602 and a downlink channel feedback information feeding back unit 604.

The multi-user channel quality indication error calculating unit 602 maycalculate multi-user channel quality indication error of a user.

Herein, the multi-user channel quality indication error may reflect theerror in channel quality indication between the situation of MU-MIMOtransmission and the situation of SU-MIMO transmission of the user. Sucherror may be caused by the parameters difference (such as the signal tonoise ratio, synchronization difference, location difference and thelike) of the user in the MU-MIMO transmission.

The downlink channel feedback information feeding back unit 604 may addthe multi-user channel quality indication error to downlink channelfeedback information including PMI and CQI, and feeding the same back toa base station for scheduling.

As can be seen, in the apparatus for feeding back downlink channelfeedback information according to above embodiment, the multi-userchannel quality indication error is further fed back to the basestation, so that the error in channel quality indication between thesituation of MU-MIMO transmission and the situation of SU-MIMOtransmission of the user may be reflected more accurately.

In this way, with this apparatus for feeding back downlink channelfeedback information, the user may feed more accurate downlink channelfeedback information back to the base station, so that the base stationmay obtain CQI and modulation coding mode more suitable for the user ina more accurate manner. Therefore, the demodulation error code rate ofthe user may be reduced in the communication system and the systemperformance may be improved.

In the apparatus for feeding back downlink channel feedback informationof FIG. 6, the multi-user channel quality indication error calculatingunit 602 may calculate the multi-user channel quality indication errorbased on various suitable parameters.

For example, in an embodiment of the disclosure, the multi-user channelquality indication error calculating unit may calculate the multi-userchannel quality indication error based on the signal to noise ratio.

FIG. 7 is a schematic diagram illustrating a multi-user channel qualityindication error calculating unit according to an embodiment of thedisclosure.

As shown in FIG. 7, the multi-user channel quality indication errorcalculating unit 700 comprises: a measuring unit 702, a quantizationerror calculating unit 704, a minimum interference level calculatingunit 706, a multi-user mode signal to noise ratio calculating unit 708,and an error calculating unit 710.

Herein, the measuring unit 702 may measure channel state of the user,thereby to obtain channel information matrix and the signal to noiseratio of the user.

The quantization error calculating unit 704 may calculate quantizationerror, wherein the quantization error is a parameter reflecting theerror between the measured channel information matrix and the obtainedpre-coding matrix.

For example, the quantization error may be calculated according toequation (2) as mentioned above.

The minimum interference level calculating unit 706 may find out a userwith the minimum interference level to the user out of all the potentialpaired users to which the user may pair, and calculate the minimuminterference level.

For example, the minimum interference level may be calculated accordingto equation (3) as mentioned above.

The multi-user mode signal to noise ratio calculating unit 708 maycalculate the signal to noise ratio of the user in the situation ofmulti-user.

Specifically, the signal to noise ratio of the user in the situation ofmulti-user may be calculated by using the quantization error, theminimum interference level, and the measured signal to noise ratio.

For example, the signal to noise ratio in the situation of multi-usermay be calculated according to equation (4) as mentioned above.

The error calculating unit 710 may calculate the multi-user channelquality indication error in the multi-user MIMO transmission of theuser.

Specifically, the error calculating unit 710 may calculate themulti-user channel quality indication error based on the signal to noiseratio measured by the user and the above calculated signal to noiseratio of the user in the multi-user MIMO transmission.

For example, the multi-user channel quality indication error may becalculated according to equation (5) as mentioned above.

In this way, the multi-user channel quality indication error calculatingunit according to the embodiments of the disclosure may calculate themulti-user channel quality indication error in the situation ofmulti-user MIMO transmission of the user based on the signal to noiseratio.

In above description, the multi-user channel quality indication errorcalculating unit calculates the multi-user channel quality indicationerror based on the signal to noise ratio, however, the above descriptionis only an example, and the disclosure is not limited to this. Forexample, the calculation of the multi-user channel quality indicationerror calculating unit may also be based on the other parameters (forexample, time parameters, location parameters, and the like). Forexample, the calculation of the multi-user channel quality indicationerror calculating unit may be based on time parameters, or based on acombination of time parameters and the signal to noise ratio.

Correspondingly, an embodiment of the disclosure also provides anapparatus for user pairing in MU-MIMO transmission mode in a MIMOsystem.

FIG. 8 illustrates an apparatus for user pairing in MU-MIMO transmissionmode in a MIMO system according to an embodiment of the disclosure.

As shown in FIG. 8, the apparatus for user pairing 800 according to anembodiment of the disclosure comprises: a downlink channel feedbackinformation receiving unit 802, initial paired user selecting unit 804,a correlation calculating unit 806, and a paired user selecting unit808.

Herein, the downlink channel feedback information receiving unit 802 mayreceive downlink channel feedback information from a user.

In the embodiments of the disclosure, the downlink channel feedbackinformation received by the base station from the user may include PMI,CQI, and multi-user channel quality indication error, wherein themulti-user channel quality indication error is used to reflect thedifference in channel quality indication between the situation ofmulti-user multiple input multiple output transmission and the situationof single user multiple input multiple output transmission of the user.

As a preferable example, the multi-user channel quality indication errormay be calculated with the method according to the above embodiments ofthe disclosure.

The initial paired user selecting unit 804 may select an initial paireduser from transmitting users.

Preferably, the initial paired user selecting unit 804 may select theuser with the minimum multi-user channel quality indication error fromthe transmitting users as an initial paired user, for example.

In this specification, the transmitting users may be defined as one ormore users which are allowed to enter a MU-MIMO transmission mode out ofthe users being transmitting data currently.

The base station may decide whether a certain user may enter the MU-MIMOtransmission mode by using an existing decision strategy, for example,based on channel condition, rate requirement, current resourceallocation, and the like of the user.

The correlation calculating unit 806 may calculate the correlation ofeach paired user to each of other transmitting users, and select one ormore users as candidate paired user(s) according to the correlation.

The correlation between two users may be calculated by using any knownmethod.

For example, the correlation of each paired user to each of othertransmitting users may be calculated by using equation (6) as mentionedabove.

After calculating the correlation, the correlation calculating unit 806may select one or more users from the other transmitting users as thecandidate paired user(s) according to the calculated correlation.

In an example, the correlation calculating unit 806 may select one ormore users with the correlation below a predetermined threshold as thecandidate paired user(s).

In another example, the correlation calculating unit 806 may also selectone or more users with the minimum correlation as the candidate paireduser(s).

Next, with reference to FIG. 8, the paired user selecting unit 808 mayselect a paired user from the candidate paired user(s).

Specifically, the base station may select according to the multi-userchannel quality indication error of individual candidate paired user(s).

For example, the base station may select a candidate paired user withthe minimum multi-user channel quality indication error in the fed backdownlink channel feedback information as the paired user.

As shown in FIG. 8, the correlation calculating unit 806 and the paireduser selecting unit 808 may repeat their operations until apredetermined number of paired users have been selected.

In the above user pairing process, the base station uses the multi-userchannel quality indication error fed back by the user. In this way, inthe MU-MIMO transmission mode, the base station may implement moreaccurate pairing. Therefore, the system performance may be improved.

The above embodiments are provided to facilitate understanding of theconception of the disclosure. However, the above description is only anexample, and the disclosure is not limited to this. Variousmodifications may be made without departing from the conception of thedisclosure.

For example, in above description, the downlink channel feedbackinformation fed by the user back to the base station only includes onePMI indication (for example, corresponding to the feedback scheme ofsingle codebook). However, the disclosure is not limited to this, andthe method (apparatus) for feeding back downlink channel feedbackinformation and the method (apparatus) for user pairing according to theembodiments of the disclosure may also be applied to other feedbackschemes.

Application Example of Dual Codebook Feedback

According to the specifications of LTE-A, in 2-antenna or 4-antenna basestation configurations, a user feeds one PMI back to a base station(that is, single codebook feedback scheme), and the PMI corresponds toone pre-coding matrix. In an 8-antenna base station configuration, auser feeds two PMI back to a base station (that is, dual codebookfeedback scheme), wherein one PMI corresponds to transmission bandwidthinformation of the downlink channel and the other PMI corresponds tosub-band information in the transmission bandwidth of the downlinkchannel; the pre-coding matrix is decided by both matrixes to whichthese two PMI correspond.

The method (apparatus) for feeding back downlink channel feedbackinformation according to the embodiments of the disclosure and themethod (apparatus) for user pairing according to the embodiments of thedisclosure may also be applied to the above dual codebook feedbackscheme.

In case of using the dual codebook feedback scheme, the process ofcalculating multi-user channel quality indication error by the user isthe same to the process of single codebook feedback scheme as describedabove in connection with FIG. 3 using equations (1)-(5).

In feeding back the downlink channel feedback information, thedifference between the dual codebook feedback scheme and the singlecodebook feedback scheme is only that the feedback formats aredifferent, that is, the downlink channel feedback information fed by theuser back to the base station includes two PMI, CQI, and the multi-userchannel quality indication error in the dual codebook feedback scheme.

On the other hand, in case of using the dual codebook feedback scheme,the process of user pairing in the MU-MIMO transmission mode by the basestation is the same to the process as described above in connection withFIG. 4.

In addition, the method (apparatus) for feeding back downlink channelfeedback information and the method (apparatus) for user pairingaccording to the embodiments of the disclosure are not limited to theabove single codebook feedback scheme and dual codebook feedback scheme,and may also be extended to be applied to more other feedback schemes.

Application Example of Other Feedback Schemes

For example, in another known feedback scheme, the transmissionbandwidth is further divided into at least one sub-band. In this case,the PMI portion of downlink channel feedback information fed by a userback to a base station may include PMI corresponding to the transmissionbandwidth information, and at least one sub-band PMI individuallycorresponding to the at least one sub-band in the transmissionbandwidth.

The method (apparatus) for feeding back downlink channel feedbackinformation according to the embodiments of the disclosure and themethod (apparatus) for user pairing according to the embodiments of thedisclosure may also be applied to the above feedback scheme.

In the above feedback scheme (the PMI portion includes at least onesub-band PMI corresponding to the at least one sub-band in thetransmission bandwidth), the user may use the process according to theabove embodiments of the disclosure (for example, with reference to FIG.3 and equations (1)-(5)) to calculate corresponding multi-user channelquality indication error for each sub-band.

Therefore, in the above feedback scheme, the downlink channel feedbackinformation fed by the user back to the base station includes: PMIportion, which includes the PMI corresponding to the transmissionbandwidth information of the downlink channel, and at least one sub-bandPMI corresponding to the at least one sub-band in the transmissionbandwidth of the downlink channel; at least one multi-user channelquality indication error individually corresponding to the at least onesub-band; and at least one CQI individually corresponding to the atleast one sub-band.

Herein, the PMI and CQI corresponding to each sub-band may be obtainedbased on the SNR and channel information matrix measured by the user foreach sub-band.

On the other hand, in the above feedback scheme, the process of userpairing in the MU-MIMO transmission mode by the base station is the sameto the process as described above in connection with FIG. 4.

Obviously, in addition to the two feedback schemes proposed above asexamples, the method (apparatus) for feeding back downlink channelfeedback information according to the embodiments of the disclosure andthe method (apparatus) for user pairing according to the embodiments ofthe disclosure may also be applied to other feedback schemes or thefeedback schemes which may occur in future, and the description thereofwill be omitted for simplicity of the specification.

In addition, an embodiment of the disclosure provides a communicationterminal comprising the apparatus for feeding back downlink channelfeedback information according to the embodiments of the disclosure. Inthis way, the terminal according to the embodiments of the disclosuremay feed the multi-user channel quality indication error back to thebase station, so that the error in channel quality indication betweenthe situation of MU-MIMO transmission and the situation of SU-MIMOtransmission of the user may be reflected more accurately. Therefore,the system performance may be improved.

An embodiment of the disclosure also provides a base station comprisingthe apparatus for user pairing in MU-MIMO transmission mode in a MIMOsystem according to the embodiments of the disclosure. In this way, thebase station according to the embodiments of the disclosure mayimplement more accurate pairing in the MU-MIMO transmission mode.Therefore, the system performance may be improved.

Further, an embodiment of the disclosure provides a MIMO communicationsystem comprising at least one communication terminal according to theabove embodiments of the disclosure and at least one base stationaccording to the above embodiments of the disclosure. In this way, theMIMO system according to the embodiments of the disclosure may implementmore accurate pairing in the MU-MIMO transmission mode. Therefore, thesystem performance may be improved.

In addition, it shall be understood that various examples andembodiments described herein are exemplary, and the disclosure is notlimited to this. In the specification, terms “first”, “second”, etc. areonly for distinguishing the features described by them literally inorder to illustrate the disclosure in a manner of clarity. Therefore, itshall not deem them to have any limited meaning.

Various component modules and units of the above apparatuses may beconfigured by software, firmware, hardware or their combination thereof.Specific means and manners that may be used by the configuration arewell known to those skilled in the art, and details are omitted here. Incase of implementing the base station by software or firmware, programconstituting the software may be mounted to a computer having adedicated hardware structure from a storage medium or network (forexample, the universal computer 900 as illustrated in FIG. 9), when thecomputer is mounted with various program, the computer may executevarious functions.

In FIG. 9, a central processing unit (CPU) 901 perform various processesaccording to the program stored in the Read-Only Memory (ROM) 902 orprograms load from the storage unit 908 to the Random Access Memory(RAM) 903. In the RAM 903, store also data required when the CPU 901performs various processes. CPU 901, ROM 902 and RAM 903 are connectedfrom one to another via bus 904. Input/output interface 905 is alsoconnected to the bus 904.

The following components are connected to the input/output interface905: input unit 906 (including keyboard, mouse, etc.); output unit 907(including display, such as cathode ray tube (CRT), liquid crystaldisplay (LCD), etc., and speakers and so on); storage unit 908(including hard disc, etc.); and communication part 909 (includingnetwork interface cards such as LAN cards, modems and so on). Thecommunication unit 909 performs communication process via network likethe interne. According to requirements, drive 910 is also connected tothe input/output interface 905. Detachable medium 911 such as disc, CD,magneto-optical disc, semiconductor memory, and so on is installed onthe drive 910 based on requirements, such that the computer program readout therefrom is installed in the storage unit 908 based onrequirements.

In case of implementing the above processes by software, programsconstituting the software are installed from a network like the Internetor from a storage medium like the detachable medium 911.

Those skilled in the art should be understood that such storage mediumis not limited to the detachable medium 911 which is stored withprograms and distributes separate from the method to provide a user withprogram as illustrated in FIG. 9. The example of the detachable medium911 includes disc (including floppy disc (registered marks)), CD(including CD read only memory (CD-ROM) and digital versatile disc(DVD)), magneto-optical disc (including mini-disc (MD) (registeredmarks)) and semiconductor memory. Alternatively, the storage medium maybe ROM 902, or hard disc included in the storage unit 908 in which aprogram is stored and the program is distributed to a user with themethod including the same.

The disclosure also provides a program product storing machine readableinstruction code. When read and executed by a machine, the instructioncode may implement the method according to the embodiment of thedisclosure.

Correspondingly, a storage medium for carrying the program code storingthe machine readable instruction code is also included in thedisclosure. The storage medium includes, but not limited to, Floppydisk, CD-ROMs, magneto-optical disk, memory card, memory stick, etc.

At last, it needs to be explained that the technical terms“comprise/include” or other variants intend to cover non-exclusioninclusion, such that process, method, article of a series of elementsare comprised, or the device includes not only those elements, but alsoother elements that are not listed evidently or further comprises theprocess, method, article or elements inherent in the device. Inaddition, in case of no more limitations, the elements defined by thesentence “comprising a . . . ” do not exclude a case that there areother the same elements in the process, method, article or deviceincluding the elements.

Although embodiments of the disclosure have been described in detail bycombining with the Figure, it shall be understood that the embodimentsdescribed above are only used to illustrate the disclosure, and do notlimit the disclosure. For those skilled in the art, the embodiments maybe changed in various manners without departing from the substance andscope of the disclosure. Therefore, the scope of the disclosure is onlydefined by the attached claims and its equivalent meanings.

1. An electronic device in a wireless communication system, comprising: processing circuity configured to measure a signal quality of a reference signal transmitted by a base station; generate a channel quality indication (CQI) and a pre-coding matrix indication (PMI) based on the signal quality; determine, based on the CQI, a difference of downlink channel quality between a sub-band transmission and a wideband transmission; and report, to the base station, a channel state information, wherein the channel state information includes the CQI and the PMI and indicates the difference of the downlink channel quality between the sub-band transmission and the wideband transmission.
 2. The electronic device according to claim 1, wherein the signal quality is a signal to noise ratio (SNR) and/or a reference signal received power (RSRP).
 3. The electronic device according to claim 1, wherein the reference signal comprises a wideband reference signal and a sub-band reference signal, and the difference of the downlink channel quality is a difference of a function value of a sub-band CQI corresponding to the sub-band reference signal and a function value of a wideband CQI corresponding to the wideband reference signal.
 4. The electronic device according to claim 1, wherein the sub-band transmission is a single user Multiple Input Multiple Output (MIMO) transmission and the wideband transmission is a multi-user MIMO transmission.
 5. The electronic device according to claim 1, wherein the electronic device is user equipment and further comprises multiple antennas configured to transmit the channel state information to the base station via a radio interface.
 6. The electronic device according to claim 1, wherein the wireless communication system is a Multiple Input Multiple Output (MIMO) communication system.
 7. A method for an electronic device in a wireless communication system, comprising: measuring a signal quality of a reference signal transmitted by a base station; generating a channel quality indication (CQI) and a pre-coding matrix indication (PMI) based on the signal quality; determining, using processing circuitry, based on the CQI, a difference of downlink channel quality between a sub-band transmission and a wideband transmission; reporting, to the base station, a channel state information, wherein the channel state information includes the CQI and the PMI and indicates the difference of the downlink channel quality between the sub-band transmission and the wideband transmission.
 8. The method according to claim 7, wherein the signal quality is a signal to noise ratio (SNR) and/or a reference signal received power (RSRP).
 9. The method according to claim 7, wherein the reference signal comprises a wideband reference signal and a sub-band reference signal, and the difference of the downlink channel quality is a difference of a function value of a sub-band CQI corresponding to the sub-band reference signal and a function value of a wideband CQI corresponding to the wideband reference signal.
 10. The method according to claim 7, wherein the sub-band transmission is a single user Multiple Input Multiple Output (MIMO) transmission and the wideband transmission is a multi-user MIMO transmission.
 11. The method according to claim 7, wherein the electronic device is user equipment and further comprises multiple antennas configured to transmit the channel state information to the base station via a radio interface.
 12. The method according to claim 7, wherein the wireless communication system is a Multiple Input Multiple Output (MIMO) communication system.
 13. A non-transitory computer readable medium including executable instructions, which when executed by a computer cause the computer to execute a method for an electronic device in a wireless communication system, the method comprising: measuring a signal quality of a reference signal transmitted by a base station; generating a channel quality indication (CQI) and a pre-coding matrix indication (PMI) based on the signal quality; determining, based on the CQI, a difference of downlink channel quality between a sub-band transmission and a wideband transmission; reporting, to the base station, a channel state information, wherein the channel state information includes the CQI and the PMI and indicates the difference of the downlink channel quality between the sub-band transmission and the wideband transmission.
 14. The non-transitory computer readable medium according to claim 13, wherein the signal quality is a signal to noise ratio (SNR) and/or a reference signal received power (RSRP).
 15. The non-transitory computer readable medium according to claim 13, wherein the reference signal comprises a wideband reference signal and a sub-band reference signal, and the difference of the downlink channel quality is a difference of a function value of a sub-band CQI corresponding to the sub-band reference signal and a function value of a wideband CQI corresponding to the wideband reference signal.
 16. The non-transitory computer readable medium according to claim 13, wherein the sub-band transmission is a single user Multiple Input Multiple Output (MIMO) transmission and the wideband transmission is a multi-user MIMO transmission.
 17. The non-transitory computer readable medium according to claim 13, wherein the electronic device is user equipment and further comprises multiple antennas configured to transmit the channel state information to the base station via a radio interface.
 18. The non-transitory computer readable medium according to claim 13, wherein the wireless communication system is a Multiple Input Multiple Output (MIMO) communication system. 